1. Field of Invention
The invention relates to a stepping motor, and in particular to a claw pole permanent magnet (PM) stepping motor.
2. Related Art
The permanent magnet (PM) stepping motor including a permanent magnet whose surface with multiple poles, is a main stream of current motor technologies. However, the surface magnetic field of the rotor is directly produced by a permanent magnet, no matter whether the rotor is formed by a single magnet or two annular magnets, because the existing rotor structure of the PM stepping motor is limited by magnet materials and the magnetization technology.
FIG. 1 is a schematic view of the rotor structure of a conventional PM stepping motor with an integrally formed magnet, and it shows the rotor structure 10 of a conventional PM stepping motor formed by an integrally formed magnet. FIG. 2 is a schematic view of the rotor structure of a conventional PM stepping motor with two annular of magnets, and it shows the rotor structure 10a of a conventional PM stepping motor with two annular magnets 20, 30. These two kinds of rotor structures are limited by the fact that the magnetization strength of magnet materials cannot be decreased, and the pole pitch between two different poles cannot be further narrowed. Take a NdFeB magnet, which has the biggest magnetization strength over other applied magnets, as a example, the surface magnetic field is only about 1000 Gauss, when the pole pitch of the NdFeB magnet is less than 1 millimeter (mm.).